CONSPICUOUSNESS OF FLOWERS 85 



In Salvia lanceolata Wi'lld., the unilateral arrangement is brought about by 

 twistings and flexures of the flower-stalks only, while the leaves maintain their 

 position. Most of the Orchids develop one-sided inflorescences in a similar fashion. 



2. Unilaterality also results from curvature of the flower-stalks in 

 compound inflorescences, e. g. in various species of Polygonatum and in 

 Scrophularia lateriflora Trautv. As in these species most of the flowers are covered 

 by leaves, and are therefore very inconspicuous, this floral arrangement must either 

 be an adaptation to special agents of pollination, or must have some unknown 

 oecological purpose. A contrast to these cases is afforded by the unilateral 

 inflorescences of Elsholzia Patrini Garcke, which also come under this heading, 

 and which are so conspicuous that they are obviously adapted to insect visits. 



3. Unilaterality of the inflorescence is conditioned by the nature 

 of the symmetry. The leaves and flowers of all species of Gladiolus are 

 primarily distichous. The kind of symmetry possessed, combined with slight 

 torsions and curvatures, produce a markedly one-sided arrangement. 



4. Unilaterality of racemes is brought about by suppression of 

 the flowers on one side of the axis. Examples : species of Vicia (V. pisi- 

 formis L., tenuifolia Roth, V. Cracca L., and others), also the species of Lathyrus, 

 which are admirably adapted to their habitat, and to the visits of insects. If their 

 inflorescences were developed on all sides, the marginal flowers at the back of the 

 cluster would be seldom or never visited by insects. 



5. Unilaterality of uniparous cymes, whether these are pure or 

 have arisen by reduction, is characteristic of the Boraginaceae, and so forth. 



6. Apically unilateral inflorescences include capitula and umbels in the 

 widest sense, and these are characteristic for whole families. 



Urban makes the following oecological deduction from his observations : 

 in a single branching plant, or in several that are near neighbours, the inflorescences 

 turn their flowers outwards in one direction, i. e. away from the centre. The result 

 is a common inflorescence exposed on all sides, and sometimes shared by various 

 individuals. It therefore follows that conspicuousness with reference to insects 

 approaching from a distance is greatly increased, and in the case of inflorescences 

 which have become unilateral by suppression, there is economy of material without 

 sacrifice of conspicuousness. And further, the oecological law for flowers that 

 the same end can be reached by the most varied means is equally applicable 

 to unilateral inflorescences. 



Conspicuousness is increased in many flowers by colour-contrast. This may 

 be exhibited either by single flowers, as in the pansy (Viola tricolor), Linaria 

 Cymbalaria, Myosotis palustris, Vicia faba. Narcissus poeticus, and others, or it may 

 be between flowers and bracts, e.g. the golden yellow corolla and the deep blue 

 bracts of Melampyrum nemorosum; or again the contrast may be between the 

 different flowers of an inflorescence, e. g. the blue ray-florets and the yellow disk- 

 florets of asters, and the like. 



It is also a highly remarkable phenomenon that, in some plants, the flowers 

 persist for a considerable time after blooming, assuming a more intense colour 

 than they previously possessed. In this way the conspicuousness of the whole 



